Design Principles

The design of a Passive House relies on the careful combination and optimization of several fundamental aspects:

Compactness

Compactness is defined as the ratio of the building envelope surface area to the enclosed volume.

• A higher compactness reduces thermal losses, improving energy efficiency.
• However, compactness should not compromise architectural quality or the urban context.
• Energy efficiency is only one factor among many that contribute to high-quality architecture.

Orientation

The building’s orientation affects energy demand by influencing solar radiation and wind exposure on the envelope.

• Proper orientation maximizes passive solar heating in winter.
• Orientation is especially critical in regions with high solar exposure, such as much of Latin America.

Solar Shading

Solar radiation provides passive heating in winter, but can create overheating issues in summer. Proper solar shading allows you to:

• Maximize solar gains during winter through window placement and glazing design
• Minimize solar heat gain in summer with overhangs, louvers, or shading devices

Increasing exterior surface reflectivity also reduces absorbed solar radiation, lowering cooling demand in summer.

A well-designed continuous thermal insulation layer within the building envelope—following the “continuous insulation (CI)” principle—significantly improves overall thermal performance, especially in winter when the temperature differential between interior and exterior is greatest, reducing heat loss to the outside.

Depending on the climate, the goal is to optimize insulation thickness to reach the point of diminishing returns, where additional thickness provides only marginal gains in energy efficiency.

The common misconception that excessive insulation negatively impacts summer performance—by trapping heat absorbed במהלך the day—is addressed through complementary passive cooling strategies, including:

• Reduced solar heat gain through proper orientation and shading design
• Effective nighttime ventilation (night flushing) to dissipate accumulated heat

Thermal mass refers to the ability of a building material in direct contact with indoor air to absorb and store heat energy until it reaches equilibrium, at which point the heat flow reverses and energy is released back into the space.

From this perspective, thermal mass can be understood as an energy buffer, functioning similarly to a thermal battery. When properly designed and optimized, this “battery” can:

• Store heat from solar gains and internal loads during the day
• Release that heat gradually when temperatures drop
• Be discharged through natural cross-ventilation or mechanical ventilation, particularly during nighttime

This process contributes to indoor temperature stability, improving occupant comfort and reducing overall heating and cooling loads.

However, thermal mass is not always beneficial. Its effectiveness depends on climate conditions, diurnal temperature swings, and building use patterns. In some cases—especially in consistently warm or humid climates—thermal mass can lead to undesirable heat retention if not properly managed.

Thermal bridges are linear or point-specific areas within the building envelope where heat flow is significantly higher than through the surrounding assemblies.

These conditions negatively impact overall energy performance and increase the risk of:

• Interstitial condensation within assemblies
• Surface condensation and mold growth

The Passive House standard emphasizes a continuous, high-performance thermal envelope, carefully designed to minimize or eliminate thermal bridging. This is achieved through proper detailing, alignment of insulation layers, and the use of thermal break materials at critical junctions.

The Passive House standard establishes strict performance requirements for windows, as they are typically the weakest component of the building envelope in terms of energy performance.

To address this, Passive House design incorporates high-performance glazing systems, including:

• Double or triple-pane insulated glazing units (IGUs), often filled with inert gases such as argon or krypton, depending on climate conditions
• Thermally efficient window frames, designed to reduce heat transfer and improve overall assembly performance

The glazing typically includes low-emissivity (low-E) coatings, which:

• Reflect heat back into the building during winter
• Reduce unwanted heat gain during summer

Windows are also selected based on a high Solar Heat Gain Coefficient (SHGC) when appropriate, allowing for:

• Maximum passive solar heat gain in winter
• Improved overall energy performance

This strategy is balanced with passive design measures, such as external shading devices, to prevent overheating and ensure optimal indoor comfort during summer months.

Controlled ventilation systems in Passive House design vary by climate and may include exhaust-only (single-flow) systems in mild climates or balanced ventilation systems (HRV/ERV) in more demanding climates.

These systems incorporate heat recovery (HRV) or energy recovery (ERV) to reclaim a significant portion of the energy from exhaust air when replacing stale indoor air with fresh outdoor air. This process helps pre-condition incoming air, reducing overall heating and cooling demand.

To maintain high energy efficiency, the Passive House standard typically targets an air exchange rate of approximately 0.3 air changes per hour (ACH) under normal operation (with higher rates possible during summer conditions).

Because a Passive House building features very high levels of thermal insulation, all construction joints must have minimal air leakage (infiltration).

Air infiltration represents unwanted and uncontrolled energy losses that are not managed by the ventilation system. It results in:

• Warm indoor air escaping to the exterior during winter
• Hot outdoor air entering the building during summer

Airtightness is a key aspect of the Passive House standard, with a significant impact on overall energy efficiency. It ensures the proper operation and performance of balanced mechanical ventilation systems with heat recovery (HRV/ERV).

Beyond energy performance, uncontrolled air leakage can cause:

• Thermal discomfort (drafts)
• Movement of moist air through building assemblies
• Increased risk of interstitial condensation and surface mold growth

Airtightness is verified through a blower door test (pressurization test). This test uses a calibrated fan installed in an exterior door or window to create a pressure difference of 50 Pascals (Pa).

To meet the Passive House standard, the building envelope must achieve an airtightness level of:

• ≤ 0.6 air changes per hour at 50 Pa (ACH50), in accordance with EN 13829.

Natural ventilation is a critical strategy for Passive House buildings in warm climates. During summer, nighttime natural ventilation (night flushing) is highly effective in dissipating the heat accumulated במהלך the day.

This approach is most effective in climates with significant diurnal temperature swings, where nighttime temperatures drop considerably compared to daytime highs.

Compliance with the Passive House standard is based on energy modeling using the PHPP (Passive House Planning Package) software.

Meeting the standard’s requirements is achieved through the optimization of the building’s energy balance—the relationship between heat gains and losses—using the PHPP calculation tool.